Apparatus for copper drossing of lead bullion



Feb. 13, 1968 v T. R. A. DAVEY ETAL APPARATUS FOR COPPER DROSSIN G OF LEAD B UL LION ZSheets-Sheet 1 Filed Dec.

1968 T. R. A. DAVEY ETAL 3,368,805

APPARATUS FOR COPPER DROSSING OF LEAD BULLION ZSheets-Sheet 2 Filed Dec. 20, 1965 United States Patent 3,368,805 APPARATUS FOR COPPER DRUSSING 0F LEAD BULLION Thomas Ronald A. Davey, Glen Waverly, Victoria, Australia, and Herbert T. Webster, deceased, late of Port Pirie, South Australia, Australia, by Emma Florence Webster, executrix, Port Pirie, South Australia, Australia, assignors to The Broken Hill Associated Smelters Proprietary Limited, Melbourne, Victoria, Australia, a corporation of Australia Continuation-impart of application Ser. No. 250,397, Jan. 9, 1963. This application Dec. 20, 1965, Ser. No. 515,254

8 Claims. (Cl. 266-37) This is a continuation-in-part of our application Ser. No. 250,397, filed Jan. 9, 1963, now Patent No. 3,260,592. Lead bullion as produced, for example, in a blast furnace, commonly contains a small proportion of copper and it is generally necessary to remove the. bulk of the copper content in order to produce lead of market grade.

The operation of separating copper, which is commonly termed copper drossing, is generally carried out by slowly cooling a batch of molten bullion. in a large open pan. The solubility of copper in lead decreases as the temperature falls, so that a copper-rich dross separates out and floats to the surface where it forms a crust which is periodically removed by skimming. This batch method of copper drossing operation involves heavy manual labour under conditions which are unpleasant and unhygienic, due both to the heat and to the evolution of fumes from the molten metal. In addition, considerable quantities of fuel are used.

Many attempts have been made to separate the copper continuously by a process in which molten bullion is caused to flow in contact with cool surfaces but these attempts appear to have met with only limited success for the reason that accretions of solid metal progressively form on the cooling surfaces and these accretions not only reduce the heat transfer efliciency but also reduce the effective volumetric capacity of the chamber in which the operation is carried out.

It is therefore an object of this invention to provide apparatus for use in continuously separating copper from molten lead bullion by a process in which copper-containing lead at a temperature substantially above 400 C., is continuously mixed with cooler and substantially copper-free molten bullion at a temperature below 400 0., whereby the mixture has an intermediate temperature of the order of 400 C., and wherein copper dross continuously separates from this mixture.

It is also an object of the invention to provide for the foregoing purpose apparatus comprising a furnace adapted to hold a bath of molten lead bullion, at least one partition wall extending upwardly from the bottom of the furnace and having its upper end disposed substantially below the operating level of the molten bullion, said partition wall sub-dividing the lower part of the furnace into a plurality of compartments comprising a mixing compartment and an inflow compartment, a pump operable to effect the withdrawal of molten bullion from the mixing compartment, means for cooling the thus withdrawn bullion to a temperature lower than 400 C. but above the melting point thereof, means for returning at least the major part of the thus cooled molten bullion to the said inflow compartment and, means for continuously discharging a proportion of said cooled molten bullion from the system.

The said mixing and inflow compartments are preferably arranged side-by-side and means are preferably provided for heating the surface of the bath of molten metal in the furnace.

The invention is hereinafter more fully described with reference to the accompanying drawings in which:

FIGURE 1 is a view in plan of continuous copper drossing apparatus according to the invention,

FIGURE 2 is a view in longitudinal section on the line 2-2 of FIGURE 1,

FIGURE 3 is a view in sectional elevation taken on the line 33 of FIGURE 1,

FIGURE 4 is a view in sectional end elevation taken on the line 4--4 of FIGURE 1,

FIGURE 5 is a view in plan of continuous copper drossing apparatus including alternative means for cooling the bullion,

FIGURES 6 and 7 are views in sectional end elevation taken respectively on the line 6-6 and 7--7 of FIGURE 5,

FIGURE 8 is a view in sectional end elevation taken on the line 88 of FIGURE 5,

FIGURE 9 is a view in elevation of an immersion cooler taken on the line 9-9 of FIGURE 8, and

FIGURE 10 is a view in sectional plan'taken on the line 1010 of FIGURE 9.

The continuous copper drossing furnace 10 shown in FIGURES 1 to 4 inclusive is of rectangular shape in plan and for the purpose of description, may be assumed to be about fifteen feet long, five feet wide and eight feet high whereby, when in use, it may contain a bath of mol ten bullion of the order of four and a half feet in depth.

The interior of the furnace is sub-divided below the free surface of the bullion by three transversely extending partition walls 12, 14 and 16 of different heights, the wall 12 being arranged about midway between the ends of the furnace and being, for example, about three feet in height, so that its upper edge is disposed about one to one and a half feet below the surface of the molten metal.

The wall 14, which is disposed about two and a half feet from one of the end walls, is about two feet high, while the third partition wall 16 is rather more than twelve inches high and is arranged between the walls 12 and 14. Thus the bottom of the furnace is sub-divided into four transversely extending compartments by submerged partition walls of different heights, these compartments being designated A, D, E, and G.

One end of compartment A communicates by an opening 18 formed in the respective side wall of the furnace,.

and close to the bottom thereof, with a recirculating pump chamber B which conveniently has its inner side formed by the furnace wall. A second external chamber C, which is separated from the chamber B by a common partition wall, communicates with the bottom of the adjacent end of the furnace compartment D by an opening 20 in the furnace wall.

A circulating pump 22 is arranged in the pump chamber B and the molten metal discharged by the pump passes into the chamber C through an opening 28 in the common partition wall below, but near the surface of, the molten metal therein.

The chamber C is a cooling chamber and for this purpose, a vertical rotary drum cooler 30 is immersed in the molten metal therein. This cooler comprises a hollow cylindrical or downwardly tapered steel drum secured to the lower end of a vertical hollow spindle 32 which is suitably supported above the furnace and arranged to be driven in any convenient manner. A fixed inlet pipe 34 for cooling water extends axially through the hollow spindle into the interior of the drum, while the water is discharged from the drum through the annular passage between this pipe and the inner periphery of the spindle. A vertical draught tube 36 is preferably arranged within the drum, and about the lower end of the water inlet pipe, to control the thermo-syphonic circulation of the water within the drum.

This rotary drum cooler is a high intensity cooling device, as high heat transfer rates can be achieved with this apparatus by maintaining high velocities of both the molten lead and water in contact with the outer and inner faces respectively of the peripheral wall thereof.

A further external chamber F arranged at the opposite side of the furnace communicates, by an opening 40 in the furnace wall, with the bottom of the adjacent end of the narrow centrally located furnace compartment E. This chamber F contains a submerged discharge pump 42 for the treated bullion and is similar in construction to chamber B.

Suitable provision is made for supplying the hot bullion to the outer end portion of the compartment G from the blast furnace, and for this purpose, the top or crown of the furnace may conveniently be provided with a charge port 44. The temperature of the charged bullion is usually about 900 C. and as temperatures of this order are too high for available pumps, it may be necessary to deliver the bullion intermittently by means of ladles. Due, how ever, to the large volumetric capacity and to the consequent thermal inertia of the furnace, such intermittent supply of bullion does not preclude continuity of the copper drossing operation hereinafter described. Thus the furnace compartment G serves as a reservoir compartment for the hot bullion.

A burner 46 is arranged at the charging end of the furnace, while a discharge flue 48 is arranged at the opposite end thereof so that the hot gases sweep over the molten metal and so maintain the surface thereof at a temperature of about, say, 1100 C., whereby the layer of dross which accumulates thereon, as later described, is maintained in the molten condition.

In operation, the discharge pump 42 in the chamber F is operated to discharge molten lead from the furnace compartment E at the average rate (say, 25 tons per hour) at which it is supplied to the furnace through the charging port 44 while the circulating pump 22 in the chamber B is operated so as to withdraw the molten metal at a much higher ratesay, at 600 tons per hour-from furnace compartment A and deliver it to the cooling chamber C from which it gravitates into the bottom of the adjacent end of the transverse furnace compartment D which thus serves as an inflow compartment for the cooled bullion.

This lead, which enters this compartment D at a tem perature of, say, 380 C., flows upwardly therein at the rate of 600 tons per hour and then divides into two streams which pass over the adjacent submerged partition walls 14 and 16 into the compartments A and E respectively on opposite sides thereof. The quantity which thus passes into compartment E is determined by the discharge rate of the pump 42 in the discharge chamber F, i.e. 25 tons per hour.

The balance of the lead supplied to the compartment D thus passes into the compartment A at the rate of 575 tons per hour, where it mixes with the hot bullion which flows downwardly therein from the surface at the rate of 25 tons per hour. This incoming bullion in the example under consideration is maintained at a temperature of about 1100 C., so that the mixture has a temperature of about 410 C. Thus lead at a temperature of 410 C. enters the cooling chamber C at the rate of 600 tons per hour and leaves that chamber at a temperature of 380 C.

The hot bullion supplied, as above explained, to the right-hand compartment G, flows at the rate of 25 tons per hour above the compartments E and D to the left-hand or mixing compartment A where it flows downwardly to mix with the cooler recirculated bullion as already explained.

Consequently, the hot incoming bullion is cooled in or above compartment A by admixture with the recirculated bullion and the zone in which this admixture takes place is disposed largely out of contact with the furnace walls.

Dross particles thus separate throughout the mass of the mixture and tend to float upwardly to the free surface of the bath, it being clear that in order to collect the dross on the surface, the rate of downward flow in the compartment A must not exceed the rate at which the dross particles float upwardly therein.

The bullion of intermediate temperature discharged from the bottom of compartment A is thus comparatively free from dross, while a further separation occurs when the cooled bullion enters compartment D from the cooler. Thus the lead which enters the compartment E for discharge from the furnace is substantially dross-free.

When the drum cooler 30 is operating correctly, the outer surface thereof has a temperature higher than the melting point of lead, so that solid lead is not deposited thereon, but accretions of higher melting point constituents, e.g. sulphides, arsenides and antimonides, could be expected to form thereon. Thus it would be necessary at intervals to remove the cooler and to replace it by another, to enable such accretions to be removed. This operation may be effected by a machining operation or, in the case of a downwardly tapered drum, by forcing the collar of solid deposits therefrom by means of a hydraulic ram.

FIGURES 5 to 10 inclusive show the substitution of alternative and preferred means for cooling the circulating bullion, though such alternative cooling means as illus' trated include features which are described and claimed in the specification of Patent No. 3,182,716 issued May 11, 1965. The continuous copper drossing furnace and the associated external chambers shown in FIGURES 5, 6 and 7 are substantially the same as that shown in the preceding figure, and the corresponding parts thereof are designated by the same references. However, the chamber C in this case merely forms a well for the return of the cooled bullion to the interior of the furnace so that it does not contain a cooling device such as the rotary cooler 30 previously described, nor does this chamber C communicate directly with the adjacent chamber B.

An external elongated open launder 50 of U shape in plan is disposed above the level of the bullion in the furnace and one of its ends is closed and arranged adjacent to the chamber B in order that the bullion withdrawn from the furnace compartment A by the circulating pump 22 may be conveniently discharged directly into the launder through the delivery pipe 24, the interior of which is accessible through an open pot 26 as shown in FIG- URE 6. The opposite end of the launder is open and is arranged to discharge the cooled bullion directly into the top of chamber B as shown in FIGURE 7.

The launder slopes downwards at a small angle from its inlet to its discharge end and is of deep and narrow shape in cross-section as shown in FIGURE 8. For example, the channel in the launder may be about thirteen inches deep to contain molten lead to a depth of about seven to ten inches without risk of spillage, while the width may decrease downwardly from the top where it may he, say, seven to ten inches wide.

The launder normally accommodates a plurality of hollow immersion coolers 52 arranged in series along the length thereof and centrally between the sides thereof.

The coolers 52 are conveniently of vertical plate-like form as shown, and may, for example, be about 24 inches in length, 16 inches in height, and 2 inches in thickness, and are arranged with their lower ends disposed close to, but above, the bottom of the launder channel. The top of each cooler is fitted with inlet and outlet pipes 54 and 55 respectively for cooling water and the interior thereof is provided with suitable baffles 53 to cause the water to pass therethrough in a predetermined path. The side and end faces of the cooler preferably taper downwardly to some extent as shown thereby to facilitate the separation of the solid accretions therefrom.

Each cooler is suspended from a corresponding vertical pneumatic ram 58 mounted on a frame structure 60 in order that the cooler may be withdrawn from, and replaced in, the launder while angular movements of the cooler are prevented by spaced vertical guide rods 59 which extend upwardly therefrom and slidably through fixed sleeves 61 on the said frame structure.

As the molten metal flows past the immersed coolers 52, a layer 57 of metal, which progressively increases in thickness, forms on each of them. These solid accretions, which extend around the sides and ends of the coolers in the form of an envelope, reduce the rate of heat transfer and also reduce the effective cross-sectional area of the channel, thus producing a rise in the level of the molten metal therein. It is necessary, therefore to remove these accretions at suitable intervals and this may be accom-- plished by cutting off the flow of cooling water to each cooler in turn so that the solid accretions thereon are remelted.

Preferably, however, each cooler is lifted out of the launder in turn by operating the respective pneumatic ram 58. See FIGURE 6, which shows one of the coolers in the raised position. The flow of cooling water through the coolers continues when the latter are raised and the resulting thermal contraction, in conjunction with the downwardly tapered form of the coolers, tends to cause the accretions to drop back into the channel in which they are wholly or partly remelted.

The coolers shown in the drawings are extended at both ends by solid vertical wings 53. These wings do not cool as quickly as the water cooled bodies 52 when the latter are withdrawn so that zones of weakness are produced in the enveloping layer 57 of metal accretions near the junctions between the wings and the water cooled bodies and this facilitates the desired separation of the accretions.

Irrespective of the manner in which the accretrons are removed, this operation is preferably carried out successively with different coolers so that the total cooling effect is not greatly reduced at any one time.

The rate at which heat is removed from the molten metal may thus be regulated by varying the number of cooling plates immersed in the molten metal and/or by varying the time between the successive operations of removing the accretions therefrom. Thus the method and apparatus permits of effective regulation of the temperature of the metal discharged from the chant.

Referring now to FIGURE 7, a propeller type agrtator or stirrer 62 is immersed in the chamber C. to prevent choking of the upper part thereof by unmelted portions of the solid metal removed from the coolers 52 while an inclined updraught tube 64 is provided to discharge the molten metal from the bottom of the furnace compartment E to the chamber F from which it is delivered by pump 66 into the holding kettle 68.

We claim: 1. Apparatus for use in continuously separating copper from lead bullion comprising:

a furnace adapted to hold a bath of molten bullion, at least one partition wall extending upwardly from the bottom of the furnace and having its upper end disposed substantially below the operating level of the molten bullion, said partition wall sub-dividing the lower part of the furnace into a plurality of compartments comprising a mixing compartment and an inflow compartment, a pump operable to effect the Withdrawal of molten bullion from the mixing compartment, means for cooling the thus withdrawn bullion to a temperature lower than 400 C. but above the melting point thereof, means for returning at least the major part of the thus cooled molten bullion to the said inflow compartment and, means for continuously discharging a proportion of said cooled molten bullion from the system.

2. Apparatus for use in continuously separating copper from lead bullion comprising:

a furnace adapted to hold a bath of molten bullion with a continuous free upper surface,

a plurality of spaced partition walls extending upwardly from the bottom of the furnace and having their upper ends disposed substantially below said free upper surface of the molten bullion, said partition walls sub-dividing the lower part of the furnace int-o a plurality of compartments comprising a mixing compartment, an inflow compartment adjoining the mixing compartment, and a reservoir compartment,

a pump operable to effect the withdrawal of molten bullion from the mixing compartment,

means for cooling the thus withdrawn bullion to a temperature lower than 400 C. but above the melting point thereof,

means for returning at least the major part of the thus.

cooled molten bullion to the said inflow compartment, and

means for continuously discharging a proportion of said cooled molten bullion from the system. I

3. Apparatus for use in continuously separating copper from lead bullion comprising:

a furnace adapted to hold a deep bath of molten bullion with a continuous free upper surface,

partition wall means extending upwardly from the bottom of the furnace to a position disposed substantially below said free upper surface of the molten bullion, said partition wall means sub-dividing the lower part of the furnace into a plurality of compartments comprising a mixing compartment, an inflow compartment adjoining the mixing compartment, a discharge compartment adjoining the inflow compartment, and a reservoir compartment,

a pump operable to effect the withdrawal of molten bullion from the mixing compartment, means for cooling the thus withdrawn bullion to a temperature lower than 400 C. but above the melting point thereof,

means for returning the thus cooled molten bullion to the said inflow compartment; and

means for continuously discharging a proportion of said returned cooled molten bullion from said discharge compartment.

4. Apparatus for use in continuously separating copper from lead bullion comprising:

a furnace adapted to hold a bath of molten bullion,

a plurality of partition walls extending upwardly from the bottom of the furnace and having their upper ends disposed substantially below the operating level of the molten metal, said partition walls sub-dividing the lower part of the furnace into a plurality of compartments comprising a reservoir compartment for hot molten bullion at a temperature substantially above 400 C., an inflow compartment for cooled molten bullion at a temperature below 400 C., and a mixing compartment adjoining the inflow compartment,

a recircuiating chamber arranged externally of the furnace and communicating freely with said mixing compartment by a submerged passage,

a recirculating pump operable to effect the withdrawal of molten bullion from said recirculating chamber,

means for cooling the thus withdrawn bullion,

means for returning the resultant cooled molten bullion to the said inflow compartment; and

means for continuously discharging a proportion of said cooled molten bullion from the system.

5. Apparatus for use in contniuously separating copper from lead bullion comprising:

a furnace adapted to hold a bath of molten bullion,

a plurality of partition walls extending upwardly from the bottom of the furnace and having their upper ends disposed substantially below the operating level of the molten metal, said partition walls sub-dividing the lower part of the furnace into a plurality of compartments comprising; a reservoir compartment for hot molten bullion at a temperature substantially above 400 C., an inflow compartment for cooled molten bullion at a temperature below 400 C., and a mixing compartment adjoining said inflow compartment,

a recirculating chamber arranged externally of the furnace and communicating freely with said mixing compartment by a submerged passage,

a recirculating pump operable to effect the withdrawal of molten bullion from said recirculating chamber,

means for cooling the thus withdrawn bullion,

a second external chamber communicating by a submerged passage with the said inflow compartment,

means for delivering the cooled molten bullion to said second external chamber whereby it flows therefrom into said inflow compartment; and

means for continuously discharging a proportion of said cooled molten bullion from the system.

6. Apparatus for use in continuously separating copper from lead bullion comprising:

a furnace adapted to hold a deep bath of molten bullion with a continuous free upper surface,

a plurality of spaced parallel partition walls extending upwardly from the bottom of the furnace and having their upper ends disposed substantially below said free upper surface of the molten metal, said partition walls sub-dividing the lower part of the furnace into a plurality of compartments comprising, in series side-by-side, a reservoir compartment for hot molten bullion at a temperature substantially above 400 C., a discharge compartment, an inflow compartment for cooled molten bullion at a temperature below 400 C., and a mixing compartment,

a recirculating chamber arranged externally of the furnace and communicating freely with said mixing compartment by a submerged passage,

a recirculating pump operable to effect the withdrawal of molten bullion from said recirculating chamber,

means for cooling the thus withdrawn bullion,

a second external chamber communicating by a submerged passage with said inflow compartment for returning the resultant cooled molten bullion to the latter,

a third external chamber communicating by a submerged passage with said discharge compartment; and

a second pump for continuously discharging a proportion of said cooled bullion from said third chamber.

7. Apparatus according to claim 6 wherein the top of that partition which separates the reservoir compartment from the discharge compartment is disposed above the level of the top of that partition which separates the mixing compartment from the inflow compartment, and wherc in the top of the last mentioned partition is disposed above the level of the top of that partition which separates the inflow compartment from the discharge compartment.

8. Apparatus for use in separating copper from lead bullion comprising a furnace adapted to hold a deep bath of molten bullion,

a plurality of spaced partition walls extending upwardly from the bottom of the furnace and having their upper ends disposed below the operating level of the molten metal, said partition walls sub-dividing the lower part of the furnace into a plurality of compartments, including a reservoir compartment, a mixing compartment and an inflow compartment for cooled bullion,

an elongated launder arranged externally of the furnace and above the level of the bullion therein,

a pump operable to deliver bullion from the lower portion of the mixing compartment into one end of said launder,

means for gravitationally returning bullion from said launder to the said inflow compartment,

means for cooling the bullion as it flows through the launder; and

means for continuously discharging a proportion of the cooled bullion from the system.

References Cited UNITED STATES PATENTS 1,687,187 10/1928 Williams 266- 34 1,886,938 11/1932 Brett et al. 75-63 X 2,648,715 8/ 1953 Lillienberg 266-34 X 2,859,958 11/1958 Perieres 266-37 FOREIGN PATENTS 46,272 11/ 1961 Poland.

J. SPENCER OVERHOLSER, Primary Examiner.

E. MAR, Assistant Examiner. 

1. APPARATUS FOR USE IN CONTINUOUSLY SEPARATING COPPER FROM LEAD BULLION COMPRISING: A FURNACE ADAPTED TO HOLD A BATH OF MOLTEN BULLION, AT LEAST ONE PARTITION WALL EXTENDING UPWARDLY FROM THE BOTTOM OF THE FURNACE AND HAVING ITS UPPER END DISPOSED SUBSTANTIALLY BELOW THE OPERATING LEVEL OF THE MOLTEN BULLION, SAID PARTITION WALL SUB-DIVIDING THE LOWER PART OF THE FURNACE INTO A PLURALITY OF COMPARTMENTS COMPRISING A MIXING COMPARTMENT AND AN INFLOW COMPARTMENT, A PUMP OPERABLE TO EFFECT THE WITHDRAWAL OF MOLTEN BULLION FROM THE MIXING COMPARTMENT, MEANS FOR COOLING THE THUS WITHDRAWN BULLION TO A TEMPERATURE LOWER THAN 400*C. BUT ABOVE THE MELTING POINT THEREOF, MEANS FOR RETURNING AT LEAST THE MAJOR PART OF THE THUS COOLED MOLTEN BULLION TO THE SAID INFLOW COMPARTMENT AND, MEANS FOR CONTINUOUSLY DISCHARGING A PROPORTION OF SAID COOLED MOLTEN BULLION FROM THE SYSTEM. 